Asian Cardiovasc Thorac Ann 2002;10:89-91
© 2002 Asia Publishing EXchange Pte Ltd
Power Doppler Imaging for Detection of Harvest Injury of Internal Mammary Artery
Yoshihiro Suematsu, MD,
Shinichi Takamoto, MD,
Toshiya Ohtsuka, MD,
Noboru Motomura, MD,
Takeshi Miyairi, MD
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Department of Cardiothoracic Surgery University of Tokyo Tokyo, Japan
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Yoshihiro Suematsu, MD Tel: 81 3 5800 8654 Fax: 81 3 5684 3989 email: suematsu{at}aurora.dti.ne.jp Department of Cardiothoracic Surgery, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8655, Japan.
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ABSTRACT
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Harvest injury of the internal mammary artery can lead to early thrombosis, which may be difficult to differentiate from atherosclerosis or harvest spasm in some cases. We describe the efficacy of intraoperative evaluation of the internal mammary artery by power Doppler imaging during off-pump or minimally invasive direct coronary artery bypass grafting.
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INTRODUCTION
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There is clear evidence that coronary artery bypass grafting (CABG) with an internal mammary artery (IMA) produces better long-term patency and beneficial effects, and that left internal mammary artery (LIMA) grafting has a strong protective effect in terms of perioperative mortality.1 CABG without cardiopulmonary bypass has been developed as an alternative technique for myocardial revascularization in high-risk patients.2 However, com-pared with conventional CABG, performing the graft-tocoronary anastomosis, as well as harvesting of the LIMA, is more difficult, especially in minimally invasive direct coronary artery bypass grafting (MIDCAB). Some conduits fail if unrecognized harvest injury, which may lead to early thrombosis, is sustained during preparation. In addition, it may be difficult to differentiate harvest injury from atherosclerosis of the LIMA or harvest spasm in some cases. There is no proven reliable technique for the intraoperative assessment of the LIMA. Power Doppler imaging (PDI) has been reported to be a feasible method during CABG,3 and we have also shown that PDI can accurately measure the diameter of graft anastomoses as well as detect technical errors and inadequacies during off-pump coronary artery bypass grafting (OPCAB).4 We describe the intraoperative evaluation of the LIMA by PDI during MIDCAB or OPCAB and the assessment of the reliability of this technique.
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TECHNIQUE
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Before applying the technique in clinical examinations, we conducted a preliminary validation study to ascertain its accuracy since few publications have described the use of intraoperative PDI for assessing the IMA. The luminal diameter of the LIMA at the level of the 4th intercostal space in 20 anesthetized mongrel dogs (weight, 15 to 21 kg) was determined by PDI and by histological examination. Measurements made by the 2 methods were compared as described elsewhere.5
In the clinical study, 10 LIMAs in 10 patients undergoing an elective MIDCAB (4 patients) or OPCAB operation (6 patients) were studied. There were 9 males and 1 female, and the mean age was 69.2 ± 8.1 years (range, 60 to 81 years). One patient was undergoing reoperation. The target vessel was the left anterior descending artery in all cases. Standard anesthetic management was applied, and the heart was exposed through a median sternotomy or a small left thoracotomy. The LIMA was dissected and skeletonized from its origin to its bifurcation and wrapped with gauze soaked in papaverine solution. Segmental arterial branches were individually clipped and divided distally using electrocautery. The quality of the LIMA was assessed by PDI. In MIDCAB, the IMA was scanned from the portion of the IMA directly visible in the operative field to the proximal portion. The presence of an intimal flap in the IMA and no Doppler signals in the pseudolumen indicate dissection, that is, harvest injury, of the IMA. The prototype imaging probe (Aloka Co. Ltd., Tokyo, Japan) has a scanning frequency of 13 MHz, a depth of field of 2 cm, and a 2-point phantom resolution of 0.1 mm. It can be sterilized by standard ethylene oxide techniques according to the directions for use. The probe is covered with a sterilized pack and sterilized jelly, which allow clear visualization of the LIMA, and it is connected to a scanner (SSD-5500; Aloka Co. Ltd., Tokyo, Japan). The maximum lumen diameter of the LIMA was measured intraoperatively by PDI and postoperatively by angiography.
StatView Software version 5 (SAS Institute, Cary, NC, USA) was used for statistical analysis. Linear regression analysis was used to correlate paired data sets. Differences were considered significant when p < 0.05.
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RESULTS
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In the animal study, luminal diameter measurements of the LIMA determined by PDI and determined histologically showed a significant correlation (Figure 1
). In the clinical study, high-quality echocardiographic images were easily obtained in the patients. The maximum luminal diameter measurements of the LIMA determined by PDI and angiography are compared in Figure 2, and an excellent correlation was found. Harvest injury was detected in 1 case only (Figure 3). There were no com-plications related to the imaging, such as coronary vessel injury or compromise, infection, or electromechanical injuries.
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Figure 1. Comparison of the maximum luminal diameter measurements of the left internal mammary artery determined by power Doppler imaging against histological measurements in an animal validation study (n = 20).
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Figure 2. Comparison of the maximum luminal diameter measurements of the left internal mammary artery determined by power Doppler imaging against angiographic measurements (n = 10).
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Figure 3. Power Doppler image of a longitudinal section of the left internal mammary artery showing dissection of the artery.
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DISCUSSION
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Using echocardiography to visualize the coronary arteries in closed-chest patients has been attempted. Recently, Ishikura and coworkers6 demonstrated the efficiency of PDI in visualizing the coronary arteries in clinical settings. Power Doppler ultrasonography, which is based on the total integrated power of the Doppler spectrum, has several advantages over conventional color Doppler echocardio-graphy: it is more sensitive to the visualization of smaller vessels, is angle-independent, and does not produce signal aliasing.7
Since the MIDCAB procedure has a limited operative field because of the small skin incision made, it is relatively difficult to examine the IMA. The imaging probe has a 36 x 10 mm contact surface, which allows deep insertion into the pleural cavity and evaluation of the IMA over its entire length. Even in a full sternotomy procedure such as conventional CABG or OPCAB, intraoperative PDI still has advantages in IMA harvesting. In addition, PDI can be applied to non-skeletonized IMA grafts, although all the IMA grafts in this study were skeletonized. The tissue surrounding the IMA does not impede visualization by PDI. Therefore, the technique described here is a valuable and reliable method for the routine detection of harvest injury of the IMA.
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REFERENCES
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ABSTRACT
INTRODUCTION
